The present invention relates to a fuel cell and, more particularly, to a system and method for controlling the humidity level of a fuel cell.
Fuel cells have been used as a power source in many applications. Fuel cells have also been proposed for use in electrical vehicular power plants to replace internal combustion engines. A solid-polymer-electrolyte fuel cell includes a membrane sandwiched in a layered relationship between an anode and a cathode. To produce electricity by way of an electrochemical reaction, hydrogen (H2) is supplied to the anode and air or oxygen (O2) is supplied to the cathode. In a first half-cell reaction, dissociation of the hydrogen (H2) at the anode generates hydrogen protons (H+) and electrons (exe2x88x92). The membrane is proton conductive and dielectric. As a result, the protons are transported through the membrane while the electrons flow through an electrical load connected across the electrodes. In this manner, electricity is produced. In a second half-cell reaction, oxygen (O2) at the cathode reacts with protons (H+), and electrons (exe2x88x92) are taken up to form water (H2O).
To operate efficiently or, in other words, produce a maximum amount of electricity, the fuel cell must be properly humidified. As a result, the hydrogen stream and/or the air stream are typically humidified by one of several methods known in the art. However, known humidification methods are prone to providing too much or too little humidification to the fuel cell through the hydrogen and air streams. Providing too much humidity to the fuel cell blocks the access of the reacting gases to the catalyst thereby impeding the electrochemical reaction between the hydrogen and air and reducing the production of electricity. Providing too little humidity to the fuel cell restricts or limits the proton transportation required for reaction within the fuel cell. Accordingly, it would be desirable to provide a system and method for controlling the humidity level of a fuel cell.
The present invention provides a system for controlling the humidity level of a fuel cell. The system includes a fuel cell, a humidifier for humidifying the fuel cell, and a controller for determining the humidity level of the fuel cell and controlling the humidifier in response to the determined humidity level. The resistance of the fuel cell varies as a function of the humidity level of the fuel cell. Thus, in a preferred system, the controller calculates the resistance of the fuel cell to determine the humidity level of the fuel cell.
The present invention also provides a method for controlling the humidity level of a fuel cell. The steps of the method include: determining the humidity level of the fuel cell, and humidifying the fuel cell in response to the determined humidity level. In a preferred method, the step of determining the humidity level of the fuel cell includes calculating the resistance of the fuel cell.